The present invention relates to a thin film transistor liquid crystal display (TFT-LCD).
Electrostatic discharge (ESD) breakdown is a critical factor affecting the yield of TFT LCD products and may cause severe damage to the products. Although some means, such as use of ionic wind for eliminating electrostatic, have been adopted in manufacturing process, electrostatic breakdown phenomena still exists.
A TFT LCD comprises a color filter substrate and a TFT array substrate that are disposed opposite to each other. FIG. 1 is a sectional view illustrating the peripheral structure around a TFT LCD display region in a conventional technique. As shown in FIG. 1, the color filter substrate is configured on the TFT array substrate and comprises a base substrate 1 and a common electrode 2 formed on the base substrate 1. The TFT array substrate comprises a base substrate 3, a common electrode 8 on the base substrate 3, a bottom metal insulating layer 4 formed on a bottom metal layer (comprising the common electrode 8, gate lines, etc (not shown)), data lines 5 formed above the bottom metal insulating layer 4, an insulating protective layer 6 above the data line 5, a via hole 7 formed in the insulating layers (comprising the bottom metal insulating layer and insulating protective layer) above the common electrode 8, and a via hole conductive film 10 formed within the via hole 7. The color filter substrate and the array substrate are assembled using sealant 12 applied along the periphery of the display region, and the TFT array substrate is electrically connected with the color filter substrate through the common electrode 2, the via hole conductive film 10, and conductive adhesive 9 on the common electrode 8. In the peripheral structure around the TFT LCD display region, the contact resistance is large between the conductive adhesive 9 and the via hole conductive film 10 in the conductive path established with the common electrodes 2 and 8 through the conductive adhesive 9 therebetween. The via hole conductive film 10 may be a transparent conductive material, such as indium tin oxide (ITO).
FIG. 2 is a sectional view illustrating another peripheral structure around a TFT LCD display region in the conventional technique. As shown in FIG. 2, metal micro-balls 11 are used instead of the conductive adhesive to establish electrical connection between the color filter substrate and the TFT array substrate. Such a connection method using micro-balls is helpful to prevent non-uniform display (particularly to the large-scale screen) due to the unstable voltage across the color filter substrate caused by electrical conduction. Moreover, different from the method using conductive adhesive, the metal micro-balls 11 are mixed in the sealant 12 at a ratio and thus are applied along with coating of the sealant. In this case, the individual adhesive coating process is not needed any more, and the yield for TFT LCDs is improved. Thus the conductive metal micro-balls are provided in the regions for assembling the color filter substrate and the TFT array substrate, establishing electrical connection between the color filter substrate and the TFT array substrate through via holes.
The metal micro-balls 11 may also appear in regions not for assembling, where connecting lines, such as data lines, gate lines, etc, are disposed for the display region. Some of the metal micro-balls even electrically contact with the common electrode of the color filter substrate, and such contact shortens the distance between the common electrode of the color filter substrate and the data lines (or the gate lines) on the array substrate and locally forms a capacitor of small capacity, which is sensitive to electrostatic, by one or more metal micro-balls, the insulating protective layer, and data lines or gate lines. In subsequent process, the electrostatic accumulates and releases through the capacitor and possibly results in the conduction between the conductive lines and the common electrode on the color filter substrate. Such ESD causes irreparable damages such as line breakage, short-circuit, etc. FIG. 3 exemplarily shows the site liable to suffer from ESD damage.